1. Field of the Invention
The present invention relates to an apparatus and method for transmitting packet data in a communication system, and more particularly to an apparatus and method for aggregately transmitting packet data in a communication system.
2. Description of the Related Art
Typically, packet data for use in a communication system is transmitted over a transmission media of a lower layer, and a header information is positioned at the front of the packet to perform a transmission control function in a Media Access Control (MAC) layer. Such a packet transmission system adapts an additional frame to perform additional functions such as a connection control, flow control, etc., and assigns a new address to the frame to implement such additional functions.
The packet data transmission system may use idle times according to characteristics of a variety of protocols. For example, an EEE 802.11 MAC protocol using a Carrier Sense Multiple Access (CSMA), prevents a collision between frames using an idle time period such as a Distributed Inter Frame Space (DIFS) or a back-off time, and receives an Acknowledgement (ACK) signal after a lapse of a Short Inter Frame Spacing (SIFS) time after data transmission has been completed.
MAC protocols 10 require some overheads 12 used for transmitting data 14 as shown in FIG. 1. But, these overheads may deteriorate a data throughput of the MAC layer. Therefore, a header compression scheme and a packet aggregation scheme have been adapted to maintain a minimum length of such overheads.
The header compression scheme prevents a header size from being increased when a field length assigned for Internet Protocol (IPv6) addresses is increased and an option field is added.
The packet aggregation scheme is adapted to enhance the data throughput by increasing the length of transmission packets. If overheads having the same lengths are provided and the length of the transmission packet is long, the packet aggregation scheme creates a high data throughput, whereas it creates a low data throughput when the length of the transmission packet is short.
Referring to FIG. 2, overheads 16 having the same size are added to individual packets 22, respectively, to transmit data “1” 18 and data “2” 20. In this case, if the packet aggregation scheme is used, the data “1” 18 and the data “2” 20 are collected in one packet 24, and only one overhead 26 is added to the data “1” 18 and “2” 20, resulting in reduction of required resources due to the omission of one overhead.
However, the aforementioned packet aggregation scheme has the following disadvantages. First, the packet aggregation scheme must assign the same destination address to each of the packets to be transmitted. If packets having different destination addresses are collected and transmitted using a multicast or broadcast address, the packet aggregation scheme cannot receive an ACK signal, resulting in unreliable packet transmission.
Second, the packet aggregation scheme cannot provide users with high Quality of Service (QoS) characteristics. Because packets requiring such QoS characteristics have the same delay and jitter characteristics that must be maintained, a sequential packet aggregation cannot maintain the QoS characteristics.